The importance of etching aluminum and its alloys has increased significantly within the last several years. As the electronics industry has moved into production of very large scale integrated circuits (VLSI), the need for methodology which meets the requirements of VLSI production has become increasingly acute.
The high-density, i.e. fine-line, geometries necessary for VLSI circuits make it essential that etching is anisotropic to achieve faithful delineation of patterns. This can be difficult with certain etchant gases such as those containing boron trichloride which can cause undercutting of the sidewalls of aluminum patterns with resulting loss of resolution.
A second problem encountered in the plasma etching of aluminum and its alloys is that most etchant gas mixtures tend to etch a substrate more rapidly at the periphery than the center. This nonuniformity of etch results in undercutting of the aluminum at the periphery over the time period required to assure complete etching of the center.
A further problem is the residues resulting from the plasma etching of aluminum. These residues, which may be formed from two sources, i.e. the photoresist and the etchant gas itself, are extremely tenacious and very difficult to remove by conventional procedures such as organic solvents or oxygen glow discharge.
In accordance with this invention, significant improvement has been achieved in all of these problem areas.